Spectroscopy is an analytical science where the characteristics or properties of a sample substance are determined based on the spectra of energy that the sample absorbs or emits. Technological advancements in both wavelength-dispersive (WD-XRF) and energy-dispersive (ED-XRF) X-ray fluorescence instrumentation enable the spectroscopic analysis of many types of sample materials, including liquid, solid, and powdered specimens.
Sample analysis cups are used with spectroscopic instrumentation to retain the sample substances during analysis. The sample substances may be disposed in a central chamber of a sample cup. A thin film of material may be disposed across an open end of a cup to retain a sample substance within the chamber and to provide a sample surface plane which is exposed to an excitation source, such as an X-ray beam, laser diode or other energy sources. The sample substance contained in the cup is subjected to analysis when energy beams impinge upon the sample surface plane. It is essential for the surface of the thin film of material, which covers an open end of the cell body, to remain planar and taut during analysis in order to produce reliable, accurate, and precise data.
With the spectrochemical analysis of specimens that exhibit high abrogation in air, a sample cup containing a specimen may be placed within a vacuum or pressurized inert gas environment. Under vacuum conditions where pressure equalization is not implemented, the thin film of material will distend outwardly due to the differential in pressures between the area within the sample cup and the environment surrounding the sample cup, which places portions of the thin film of material closer to the source of excitation. The variation and decrease in distance from the sample surface plane to the source of excitation alters the absorption and emission of radiation from the sample specimen and the intensity of radiation impinging upon the specimen. Consequently, erroneous qualitative and quantitative data may be produced.
In applications requiring a pressurized inert gaseous environment, where pressure is greater on the outside of the sample cup than inside the sample cup, the thin film of material distends into the hollow of the sample cup providing a concave sample surface, thereby increasing the distance between the sample surface plane and the excitation source, also resulting in erroneous analytical data.
To equalize the pressure between the inside and outside of the sample cups, and to eliminate distension of the sample surface plane, some sample cups are provided with a venting means, or may include a vent hole in the top or cap of an assembled cup. The venting means may be activated or punctured to provide pressure equalization between the inside and outside of the cup. Other sample cups may include a main cell body with a double open-ended cup, which, upon assembly with a thin film, allows for continuous venting during analysis.
In addition to the problem of distention, the sample substance contained in a sample cup may escape or exude from the central chamber during analysis onto the analysis chamber, an X-ray tube, an X-ray detector, or other delicate electronic components of the instrumentation, causing damage thereto. In addition, the exuded sample substance may cause contamination issues, costly cleanups, and non-productive down time.
There remains a need for sample cups that provide a planar sample surface plane while substantially eliminating the possibility of any sample exuding from the cup during analysis, and the subsequent damage and contamination to the instrumentation.